Hypertension is defined by American Heart Association as arterial blood pressure higher than 140/90 mmHg and by the World Health Organization (WHO) as higher than 160/95 mmHg. The prevalence of hypertension in the world population is estimated at approximately 20% of all adults. No single mechanism has been identified to explain the phenomenon of hypertension, but it may result from genetic factors. This type of hypertension is designated essential hypertension and includes most of the known cases. Several cardiovascular diseases are common or more severe in humans with high blood pressure, including atherosclerosis, coronary artery disease, congestive heart failure, stroke, diabetes, and renal and retinal diseases. The purpose of the treatment of hypertension is to prevent these significant cardiovascular complications. Most importantly, effective drug therapy has been shown through controlled clinical trials to reduce the morbidity and mortality associated with high arterial pressure. Antihypertensive drugs can be divided into seven classes, i.e., diuretics, .beta.-blockers, centrally acting sympatholytics (.alpha..sub.2 -agonists), peripherally acting sympatholytics (.alpha..sub.1 -antagonists), calcium-channel blockers, orally active vasodilators and converting enzyme inhibitors. However, many side effects are observed during clinical applications of these antihypertensive agents.
Cardiac arrhythmia is a disorder of rate, rhythm, or conduction of electrical impulses within the heart. Such disorders are often associated with coronary artery diseases, e.g., myocardial infarction and atherosclerotic heart disease. Arrhythmia can eventually cause a decrease in the mechanical efficiency of the heart, reducing cardiac output. As a result, arrhythmia can have life-threatening effects that require immediate intervention. Many antiarrhythmic drugs act by blocking myocardial Na.sup.+ or Ca.sup.++ ion channels or by prolonging the cardiac action potential duration through the inhibition of potassium currents which are responsible for action potential repolarization.
Thrombosis is formed by the interaction of the damaged blood vessel wall with the blood components such as platelets and other clotting proteins. The damaged blood vessel is usually caused by elevated level of plasma cholesterol or triglyceride. When a blood vessel is damaged, the endothelium is disrupted and an underlying layer of collagen fiber is exposed. The exposed collagen attracts platelets and causes the release of ADP and the formation of thromboxane A.sub.2 which further activate platelets. Platelet aggregation is one of the main causes leading to myocardial infarction and cerebral thrombosis. In spite of the intensive research for an effective antiplatelet drug, there is no drug to date that can effectively prevent the thrombosis, except for some old drugs, such as aspirin and dipyridamole.
Lu et al. isolated dicentrine and other alkaloids from the plant Lindera oldhamii (megaphylla) Hemsl (Yakugaku Zasshi, 92; 910-917, 1972), but they did not show any biological activity of these compounds.